A sum of money doubles itself in 7 years.In how many years will it become 4 times at SI
(a) 15
(b)21
(c)18
(d)25
ah yes i see the problem I used compound interest.
simple interest you do no get interest on the interest.
So if sum of money = x
Every 7 years you will get x interest
after 7 years you have x + x
After 14 years you have x + x + x
After 21 years you have x + x +x +x =4x